For example, some headlamps disposed on the left and right of the front portion of a vehicle are configured so as to obtain a desired light distribution by guiding light having a high directivity emitted from a light-emitting diode (LED) to the inside of a light guiding body and causing the light to be outputted from the light guiding body. Examples of such headlamps may include those disclosed in Japanese Patent Application Laid-Open Nos. 2014-154219 and 2016-004667. One of examples of such a vehicular lamp is shown in FIG. 1.
FIG. 1 is a cross-sectional side view of a conventional vehicular lamp, and the illustrated vehicular lamp 101 is used as a headlamp. As illustrated in FIG. 1, the vehicular lamp 101 is configured to include an LED 105 serving as a light source, a light source substrate 106a for use in mounting the LED 105, a control substrate 106b for driving and controlling the LED 105, a light guide inner lens 107 of such as a rod, a prism, a plate, or a different shape which is a light guiding body arranged horizontally along the vehicle front-rear direction (left-right direction in FIG. 1), and an extension 108 arranged around the light guide inner lens 107, which are all accommodated in a lamp chamber 104 defined by a housing 102 and a transparent outer lens 103 covering the front opening of the housing 102.
The light guide inner lens 107 is disposed substantially at the center in the lamp chamber 104, and has a parabolic incidence surface 107a formed at the rear end thereof in the longitudinal direction (right end in FIG. 1). The light guide inner lens 107 further has a two-step curved emission surface 107b having cuts for use in controlling light distribution and formed at the front end in the longitudinal direction (left end in FIG. 1). The light guide inner lens 107 is fixed to the extension 108 at the middle portion in the longitudinal direction.
The light guide inner lens 107 has a boss 107c formed at the longitudinal rear end of the light guide inner lens 107. The light source substrate 106a of a flat plate shape is fixed to the boss 107c. The LED 105 mounted on the light source substrate 106a faces the incident surface 107a of the light guide inner lens 107.
The control substrate 106b of a flat plate shape is vertically fixed to the housing 102 at the rear of the light source substrate 106a. Here, an external input connector 109 is inserted through and held in the rear wall of the housing 102, and a maintenance hole 102c is formed in a predetermined portion of the bottom wall of the housing 102 (a position below the light source substrate 106a and the control substrate 106b). The hole 102c is normally closed by a cap 115.
Furthermore, the light source substrate 106a and the control substrate 106b are electrically connected to each other by a cord 112, and the control substrate 106b is electrically connected to the external input connector 109 held by the housing 102 by another cord 113. The external input connector 109 is electrically connected to a power source (not illustrated) such as a battery by a code (not illustrated).
In the vehicular lamp 101 configured as described above, when electric power is supplied from a battery (not illustrated) to the LED 105 through the external input connector 109, the cord 113, the control substrate 106b, the cord 112, and the light source substrate 106a, the LED 105 is activated to emit light. The light emitted from the LED 105 toward the front of the vehicle (left side in FIG. 1) enters the light guide inner lens 107 through the incident surface 107a of the light guide inner lens 107. The light having entered the light guide inner lens 107 travels as parallel light toward the front of the vehicle in the light guide inner lens 107, and exits through the emission surface 107b of the light guide inner lens 107 toward the front of the vehicle while being diffused to the periphery. In this manner, the light distribution is controlled, so that the light passes through the transparent outer lens 103, and is irradiated toward the front of the vehicle. As a result, the vehicular lamp 101 functions as a headlamp.
Here, a method of assembling the vehicular lamp 101 will be described below with reference to FIGS. 2 and 3.
FIG. 2 is a cross-sectional side view illustrating a state before assembly of a conventional vehicular lamp, and FIG. 3 is a cross-sectional side view illustrating a state during assembly (cord connection) of the vehicular lamp. In assembling the vehicular lamp 101, before assembling the outer lens 103 to the housing 102, as shown in FIG. 2, the outer lens 103, the extension 108 accommodated therein, a lens unit U1 composed of the light guide inner lens 107 fixed to the extension 108 and the light source substrate 106a fixed to the light guide inner lens 107, and a housing unit U2 composed of the control substrate 106b fixed to the housing 102 are individually prepared. As shown in FIG. 3, the lens unit U1 and the housing unit U2 are assembled; however, in a state where both units have been assembled in this manner, one end of the cord 112, the other end of which has been connected to the light source substrate 106a, is in a free state, so that it is necessary to connect the one end of the cord 112 to the control substrate 106b. As shown in FIG. 3, this operation is performed by removing the cap 115 fixed to the housing 102 to open the maintenance hole 102c formed in the housing 102, and inserting a hand of an operator into the housing 102 through the hole 102c to connect the cord 112 to the control substrate 106b. 
However, in the conventional vehicular lamp 101 illustrated in FIG. 1, it is necessary to detach the cap 115 and connect the cord 112 to the control substrate 106b in a state where the lens unit U1 and the housing unit U2 are assembled as illustrated in FIG. 3. Accordingly, there has been a problem that, in addition to the troublesome operations and increased assembly process steps, the number of components increases because the cord 112 and the cap 115 are necessary, resulting in cost increase.